its the depth that does it, it is 35 feet deep, it is very decieving, I had to go deep , because I needed alot of fill and could only make my pond this size because any bigger and it would have been out of specs and would have been too close to my septic, or to close to the golf course and other property for code - which meant instead of digging left, right, I had to dig straight down, 36 feet straight down to be exact.